In a large pot, heat olive oil over medium heat. Add chopped leeks and minced garlic, sauté until leeks are softened, about 5 minutes
Add sliced mushrooms to the pot and cook until they begin to soften and release their juices, about 8 minutes.
Reduce heat to low and stir in heavy cream if using. Cook for an additional 2 minutes. Adjust seasoning as needed before serving.